I have read posts back into 2012 on this subject because the rubber has hit the road for me-I want to run three or perhaps four monitors (Samsung Synchromasters-22") on my beloved Mac Pro. MY Radeon 2660 is still running ok, but, of course won' support more than two displays. Based on another thread here, I'm planning on getting a GTX 650 and running both cards. I run Mountain Lion because I use the "spaces" capability of that system which appears to not be available in Yosemite. I am not a gamer, but use a streaming trading system that likes to have multiple monitors. I'm a retired techie, but have just had a need to use a tech service to recover some files that I lost in a re-setup of boot camp on one disk. He has counseled me to not use the GTX 650, saying it will not run reliably on my system and that my monitors may not work. At this, my tech background takes that as a challenge and I have a source for the GTX card that allows for a 30 day return. Nevertheless, I thought I'd put up query here to get one last confirm before moving ahead as there maybe someting about my configuration of monitors, or my planning to use both graphics cards that will catastrophic. Comments will be greatly appreciated.